1. Field of the Invention
The present invention relates to an improved air induction unit for reducing noises emitted from an engine and a temperature rise of intake air.
2. Description of the Related Art
European Patent 0523028B1 (U.S. Pat. No. 5,259,356) and JP-A-7-229454 (U.S. Pat. No. 5,477,819) disclose an air induction unit having a plurality of parts integrated therewith. In such systems, an intake air filter is disposed in an air filter case. The air filter has a sealed surface which is sealed and supported by the inner wall of the air filter case.
JP-A-7-148864 (U.S. Pat. No. 5,538,571) discloses an intake manifold which is blow-molded from a hollow inside portion to have a plurality of separate outside portions, which are bonded together thereafter.
Such an air filter as disclosed in European Patent 0523028B1 or JP-A-7-229454 must have a specific shape to be supported by the inside wall of the air filter case. It is sometimes difficult to install an air filter having the specific-shaped filter case together with various devices into the limited space of an engine compartment. Especially, if a plurality of parts are integrated into an air induction unit, the system becomes too bulky to be installed. Such an air filter also has the problem of passing intake air noises from air induction passages because the air induction passage has a single wall. In addition, heat radiation from the engine raises the temperature of the intake manifold and intake air, thereby deteriorating engine performance.
Because the air filter disclosed in JP-A-148864 has double walls with the outside members bonded thereto, noise and a temperature rise can be prevented to some extent. However, the effect is not satisfactory because the outside portions are merely bonded to the outer periphery of the inside portion.